This invention relates generally to signal encryption and decoder systems, and more particularly, to a system for scrambling and descrambling video signals wherein the decoding information is carried directly with the channel of interest, the system being very difficult to defeat by individual and large scale pirates.
There is a need for a video encryption system which transmits a scrambling code from a sending unit to a number of decoders at respective receiving stations, wherein the system is inexpensive and affords a high degree of security. In the field of video transmission, in particular, there is a need for a coding system which achieves the aforementioned advantages, and which is compatible with a wide variety of scrambling systems. Such adaptability of the coding scheme would address directly the issue of maintaining costs low.
It is, of course, the primary purpose of a video scrambling scheme to prevent the information content of the video signal from becoming available to unauthorized receivers. Although it is important to achieve a high measure of security against unauthorized reception by individuals, such as individual cable television service subscribers, the far greater problem is that of pirates who operate on a large scale. In this regard, it is important to recognize that absolute system security, although a worthwhile goal, is not the end to be achieved. Any coding system, no matter how secure, can eventually be defeated. However, the business of pirating video services is, like any other business, subject to certain economic principles. More specifically, the large scale pirate must always be mindful of the costs associated with overcoming a video encryption system. There is, therefore, a need for a video scrambling and descrambling system which is prohibitively expensive for the pirate to overcome on a large scale.
In addition to the foregoing, it is desirable that the cost of video scrambling and descrambling systems be reduced, such as by permitting decoders to be available to, and owned by, customers or subscribers. Such decoders should be of a type which can be enabled only by the station operator, who also should have the ability to disable any decoder at anytime.
One of the problems with present scrambling systems is that the decoding function is not active, in that the keys required to effect decoding do not change rapidly. In some such systems, a simple short circuit or jumper connection will permanently enable the decoder. There is a need for a decoder arrangement which is immune from any one-time modification which would enable same permanently. In addition, there is a need for a decoder system which avoids the possibility that a bank of switches on a pirate decoder could be set for a particular configuration which would last for a viewing period.
It is another shortcoming of currently available video security systems that a second system, such as a telephone link or a card is required to effect descrambling. In such systems, two keys are sent over different links of communication, one over the air and the other via a telephone link.
Present day television systems, such as cable franchise systems, are not amenable to impulse purchasing. In most known systems, a second communication link is required to request the desired service, such as a "pay-per-view" program, well in advance of the commencement of the scheduled program. There is, therefore, a need for a system which will permit a subscriber to accept billing for pay-per-view programming at the push of a button at the remote location.
It is, therefore, an object of this invention to provide a system which encrypts and decodes a multicomponent signal of interest, such as a video signal, with a high degree of security.
It is another object of this invention to provide a video encoding and decoding system wherein pirating of services on a large scale is prohibitively expensive.
It is also an object of this invention to provide a signal encoding system wherein the information required to achieve decoding is carried, at least in part, in the encoded signal of interest.
It is a further object of this invention to provide a video signal scrambling system wherein the system operator can remotely disable or enable ones of remote decoders, as desired.
It is additionally an object of this invention to provide a video scrambling system of the type where an operator supplies a multiplicity of remote decoders, wherein at least selectable ones of the remote decoders are automatically disabled over a predetermined period of time, unless the operator actively maintains decoder enablement.
It is yet a further object of this invention to provide a scrambled video transmission system wherein the decoding process is active, requiring rapidly periodic decoding processes to be performed on the video signal.
It is also another object of this invention to provide a video scrambling system where no additional communications links are required to transmit decoding information or keys.
It is yet an additional object of this invention to provide a video system wherein highly selective enablement, such as pay-per-view or impulse purchasing can be accommodated without requiring a communication link between the viewer and the system operator.
It is still another object of this invention to provide a scrambled video transmission system wherein security codes are changeable throughout the system without requiring interruption of the service.
It is a yet further object of this invention to provide a secure video transmission system wherein the system can be operated in a plurality of security modes simultaneously.
It is also a further object of this invention to provide a secure video transmission system having a plurality of security modes wherein the security mode is changeable throughout the system while the system remains operative to all authorized subscribers during transition from one security mode to another.
It is additionally another object of this invention to provide a signal transmission system wherein a subscriber can determine to accept a pay-per-view program directly at a remote decoder station, without the need for a second communication link.
A still further object of this invention is to provide a video coding system which can be employed with a wide variety of scrambling arrangements.
An additional object of this invention is to provide a descrambling system which cannot be overcome merely by placing an enabling jumper wire in the circuit.
Yet another object of this invention is to provide a descrambling system which employs decoders at each receiving station, wherein the decoders cannot be unauthorizedly enabled even for the duration of a viewing period.
Another object of this invention is to provide a signal scrambling and descrambling system which employs multiple decoder keys but does not rely on channels of communication other than the signal channel itself to transmit descrambling information to the decoder at the receiving station.
A yet further object of this invention is to provide a coding system for scrambling video which is compatible with a plurality of video scrambling systems.